One limiting size factor of hand-held digital devices such as a PDA (personal digital assistant) is the number of buttons on their keyboard, making it difficult for text inputting. Telephones have the same text-inputting problem via their twelve buttons. There has also been a gradual integration of PDA and phone, which underlines the need for a good method of text inputting with few buttons.
U.S. Pat. Nos. 5,392,338 and 4,658,417 are directed to inputting alphabet via the phone keypad, in which pushing a button one or more times during some period enters a character. The method is simple, easy to learn but is slow and limited in the number of characters.
The most promising system to by-pass the disadvantages of the above multi-pressed method is the two-key system, in which each character is entered via two buttons, pressed simultaneously or sequentially. Typewriter and computer keyboards have always used the system. Capitalizing, for example, is by simultaneously pressing a shift button and another button. Most computer applications support control actions on simultaneous pressing a control button and another button and many also allow menu selection by sequentially pressing an alt button and then typing another button. The two-key system is also commonly used to input non-English alphabet letters.
Knowlton, in U.S. Pat. No. 3,967,273, describes the layout of the standard QWERTY keyboard on the telephone keyboard and sets the rules for the two-key system that others build on with variations. First, encoding of each character is with two buttons, pressed sequentially. Next, each button is labeled with an array of characters. Finally, the button labeled with the character to encode is the first button and the location of the second button can be inferred from the location of the character relative to other characters on the button.
U.S. Pat. Nos. 5,117,455 and 5,339,358 describe an arrangement of characters between buttons; the sequence of activating the buttons indicates the entry of that letter or symbol.
Kandogan and his associates, in U.S. Pat. No. 6,765,556, use two buttons of the same row to input alphabet on the standard phone keypad.
Lee and associates, in patent number U.S. Pat. No. 6,802,661, describe a matrix of tables. The first button selects a table and the second button selects an entry in the table.
Bozorgui-Nesbat, in U.S. Pat. No. 6,847,706, describes a system that places the alphabet on a keyboard based on occurrence frequency.
The above methods have not gained popularity probably because either there was no need for it at the time or they involve a steep learning curve. Most have ignored characters frequently used in computing and languages not based on Latin alphabet.
All patents, patent applications, provisional applications, and publications referred to or cited herein, or from which a claim for benefit of priority has been made, are incorporated herein by reference in their entirety to the extent they are not inconsistent with the explicit teachings of this specification.